1. Field of the Invention
This invention relates to an environmentally safe process for converting waste plastic materials to valuable gas products and environmentally nontoxic slag, and more particularly to a minimum liquid discharge integrated liquefaction and gasification process for converting bulk halogen-containing waste plastic materials into a liquid hydrocarbonaceous feedstock that can be used in a partial oxidation reactor to produce a synthesis gas that is primarily carbon monoxide and hydrogen, and a non-leachable environmentally nontoxic slag.
2. Description of the Prior Art
Waste plastic materials, especially halogen-containing waste plastic materials, and particularly those with a high chloride content present especially difficult disposal problems, since these materials are subject to increasingly stringent environmental restrictions against dumping or landfill disposal. Burning the waste plastic materials is feasible only if conducted in accordance with strict environmental restrictions against atmospheric disposal of chloride-containing gases and toxic particulate by-products.
Canadian Patent Application No. 2,130,019 to Gerhardus et al. relates to a process for thermally cracking waste plastic materials which then undergo partial oxidation to produce synthesis gas. However, it is necessary to dehalogenate the waste plastic materials prior to partial oxidation because of severe corrosion problems that can occur without dehalogenation when halide-containing vapors accompanying the syngas products are cooled and condensed. The halide vapors, primarily in the form of hydrogen chloride are condensed from the gaseous degradation products which occur during liquefaction of the waste plastic materials. Dehalogenation, especially dechlorination prior to partial oxidation is an important concern because the Canadian patent relies upon radiant cooling of the partial oxidation gasification products. Therefore, the presence of hydrogen chloride or halide vapors would present severe corrosion problems in the equipment used in the process of the Canadian patent.
German Patent Application DE 4412360A1 to Rabe et al. discloses a process for recycling mixed and contaminated waste plastic materials in a gasification reaction to produce carbon monoxide and hydrogen. The German process utilizes liquefaction and gasification steps but does not address the problem of dealing with halogen-containing waste plastic materials.
As used herein, a partial oxidation reactor can also be referred to as a "partial oxidation gasifier," or simply a "gasifier," and these terms are often used equivalently and interchangeably. The partial oxidation reactors that are used in this invention are also commonly referred to as "quench gasifiers."
Reaction temperatures for partial oxidation typically range from about 900.degree. C. to about 2,000.degree. C., preferably from about 1,200.degree. C. to about 1,600.degree. C. Pressures typically range from about 1 to about 250 atmospheres, preferably from about 5 to about 200 atmospheres, most preferably about 20 to about 80 atmospheres.
Partial oxidation reactors are disclosed in U.S. Pat. No. 4,823,741 to Davis et al., U.S. Pat. No. 4,889,540 to Segerstrom et al., U.S. Pat. Nos. 4,959,080 and 4,979,964, both to Stemling, U.S. Pat. No. 5,281,243 to Leininger, and U.S. Pat. Nos. 5,554,202 and 5,545,238 both to Brooker et al.